Chapter 2: Definition Of Piracy - "Armed Robbery"

The United Nations Convention On The Law Of The Sea (UNCLOS) writes a definition of piracy like this:

"Piracy consists of any of the following acts:
A. Any illegal acts of violence or detention, or any act of depredation, committed for private ends by the crew or the passengers of a private ship or a private aircraft, and directed:
1. On the high seas, against another ship or aircraft, or against persons or property onboard such ship or aircraft.
2. Against a ship, aircraft, persons or property in a place outside the jurisdiction of any state;
B. Any act of voluntary participation in the operation of a ship or of an aircraft with nowledge of facts making it a pirateship or aircraft;
C. Any act inciting or of intentionally facilitating an act described in sub-paragraph A or B."

It reads much about violence against ships in this definition of piracy but it's clear that many acts of violence against ships (especially those in ports or in territorial waters) are NOT regarded as Piracy under international law. They are classified as "Armed Robbery".
In April 1984 the MSC (Maritime Safety Committe) established "Piracy And Armed Robbery Against Ships" as a separate item in its work-programme against piracy.